Electric wave amplifier



Nov. 25, 1947 E. LABIN 2,431,333

I ELECTRIC WAVE AMPLIFIER Filed May 31, 1945 2 Sheets-Sheet 1 Nov. 25, 1947. E, LABIN 2,431,333

ELECTRIC WAVE AMPLIFIER 1 Filed May 51, 1943 2 Sheets-Sheet 2 INVENTOR.

EMILE LABlN ATTORNEX Patented Nov. 25, 1947 ELECTRIC WAVE AMPLIFIER Emile Labin, New York, N. Y., assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application May 31, 1943, Serial No. 489,113 In France July 29, 1939 3 Claims. (Cl. 179-171) The present invention relates to modulated radio-electric wave transmission systems and has as its main object the provision of means for neutralizing a radio frequency amplifier stage so as to obtain a low input and output capacity of the stage.

The invention, in particular, in accordance with its general aspect, provides a method for neutralizing the amplifier stage, consisting of balancing a bridged-T network of which the bridge is composed of elements equivalent to the electrode impedance of the amplifier tube stage and causing the harmful reaction, by means of impedance, particularly in the construction of the shunt arm of the bridged-T.

In accordance with certain characteristics the invention provides, in a triode tube employed as a stage of a transmission circuit, the insertion of an impedance in the connection of an electrode, which is neither used as input electrode nor output electrode, the value of this impedance being defined by the balance relation of the equivalent bridged-T network in which the bridge is composed of the impedance between electrodes of the tube and the shunt arm by this inserted impedance.

In the drawings hereunto attached:

Fig. 1 is a diagram illustrating the broad aspect, and especially the mathematical quantities involved in this invention.

Fig. 2 shows one embodiment of this invention, employing a neutralizing impedance in the grid circuit of a triode.

Fig. 3 shows another form of this invention, using a neutralizing impedance in the filament circuit of a triode.

Fig. 4 shows yet another embodiment, wherein a neutralizing inductance is employed in the anode circuit.

Fig. 5 shows the embodiments shown in Fig. 4

' wired as an amplifier.

An example of a neutralizing of this type is shown in Fig. 1 and the relation giving the equilibrium of the bridge is given in the form:

that of the tube to be neutralized, although strictly speaking the two terminals of the grid and plate filament do not exist, since the complicated geometrical structure of the tube cannot be replaced by a circuit formed of short-circuited elements.

In Fig. 1, R1,'R2 and R3 between the two terminals 1 and 3 represent the inter-electrode impedan ces of the tube, R4 represents the neutralize impedance and the impedances of the connections to the tube elements are indicated at R5 and Rs between the connected terminals I and 3 and the accessible terminals 5 and 6 of the tube, respectively.

For the reactances, the above formula of equilibrium of the bridged-T network may be applied.

For low frequenc es it is possible to assume as zero the reactances R5 and Re, the reactance R4 as only comprising the neutralizing impedance, and the reactances R1, R2 and R: may be assumed to be reduced to capacitances between the electrodes of the tube.

For higher frequencies applicant has found that the reactances R5 and Re will have to be considered, as they are composed of the inductances of the connections, the reactance R; as comprising also the inductance of the connection, the reactances R1, R2 and R3 still being reduced to the inter-electrode capacitances of the tube.

For still higher frequencies the precise length of the electrodes must be taken into consideration with respect to the operative wave length and the mutual inductance between these electrodes, by introducing for the reactances R1, R2 and R inductances in series or in parallel with the capacities proper of the electrodes of the tube. In all cases it is possible to constitute with the tube under consideration a bridged-T network of thetype of Fig. 1, and this network may be calculated in the manner above indicated. Consequently, the balancing formula given above may be applied in all cases, this formula not being dependent u on the order of the electrodes with respect to the bridged-T network, nor on the nature of the reactances themselves of the tube. It should, however, be noted that if there is always a solution to the balanced relation when the various impedances of the bridge re reactances, the same may no longer be the case if complicated impedances are introduced into the network, i. e. if there are resistive components in the impedances of the tube, because then there would have to be employed in the shunt branch a compensation resistance with negative characteristic, and it may not always be possible to arrange the negative resistance so as to be capable of compensating the resistance of the bridge of the network, the characteristics as to negative resistance of an element not actually being sufiiciently flexible to allow such a possibility.

Apart from this exception, the above relation means thatit is nearly always possible'to find a reactance R4 which neutralizes the output terminal 2 with respect to the input terminal I.

This method of neutralizing is described in detail for a connection of electrodessuch as that indicated in Fig. 2. In this drawing and the iollowing ones the filament or cathode of the tube is designated by F, the grid by G, and the anode by P. The tuned input and output circuits are indicated by and 0C. In Fig. 2the input of energy to the tube takes place through the filament F (terminal I of the network of Fig. 1) and the output is derived from the anode .P (terminal 3 of Fig. 1). The neutralize impedance R4 is inserted in the grid connection G.

Fig. 3 shows another method of feeding energy to the tube. In this classic method of feed, the terminal I of the network of Fig. 1 corresponds to the grid G, and the termina1'3 to the anode. The neutralized impedance R4 is inserted in the filament connection F of the tube. Neutrodynin'g is thus possible by a suitable reactance in the filament circuit in accordance with one embodiment of :this invention. Assuming that the reactances between the terminals l, 2 and 3 are reduced to the capacities of the electrodes themselves, the neutralize reactance R4 in thefilament connection will then be a simple inductance. A circuit of this-kind thus ensures the main advantage sought in the present invention, of having plate output capacities :and grid input capacities lower than those which would be-obtained in the usual neutralizing by means of a capacity bridge or the like.

In this case also, the calculations above given for deriving the inductance used for neutralizing are valid by altering the meaning .of the-capacities, as will be apparent to one skilled in the art.

As shown in Fig. 4, this invention also includes the neutralizing of a stage fed through the grid (terminal I of the network of Fig. 1) with output through the filament F (terminal 2 of Fig. 1), the anode P (terminal 3 of Fig. '1), including in the connected circuit thereof the neutralize impedance. Here again, if it be assumed that the reactances between the terminals I, 2 and 3 are reduced to capacities, the reactance R4 in the anode connection employed to secure neutralization will be a pure inductance and the input and output capacities of the stage will be of lower value than for the usual method of neutralizing by a capacity bridge or the like. The value of this inductance will also be given by the formula above stated, by correctly establishing the correspondence of the capacities and of the electrodes with the quantities stated in the formula.

This latter circuit arrangement may be particularly advantageously employed at high frequencies owing to the neutralizing provided.

the combination of the battery and condenser will have a negligible effect on the circuit. Biassing battery 9 is added between the filament F and grid G andis in series witha resistance ID. This resistance is large so that the combination will have a negligible eiTect on the balance of the bridge T network. Condenser H is inserted between the grid and the input circuit IC to block "the direct current of the plate supply battery 1 from the grid. Its capacitance is large and so it has a negligible effect on the balance of the bridge T network. Filament F may be energized in any well known manner.

Moreover, at high frequencies the nature of the neutralizing reaction to be employed may serve to determine the nature, and even to measure the value, of the reactances of the tube itself connected in accordance with the diagrams of Figs. 2, 3 or 4.

Still other modifications and applications of the invention may be made by those skilled in the art without departing from the scope of the invention. I 7

What is claimed is: f

1. Triode tube neutralization circuit including a bridge-T network comprising a tuned input circuit connected from the grid of said triode to a tie conductor, a tuned output circuit connected from the cathode of said triode to said tie conductor and a neutralizing impedance connected from the anode of said triode to said tie conductor.

2. A triode tube neutralizing circuit which is a bridge T network comprising a tuned input circuit connected from the grid of said triode to a tie conductor, a tuned output circuit connected from another electrode of said triode to said tie conductor, and a neutralizing impedance connected from the other electrode of said triode to said tie conductor, whereby said impedance balances said bridged T network.

3. A triode tube neutralizing circuit according to claim 2 in which the tuned output circuit is connected from the anode of said triode to said tie conductor and the neutralizing impedance is connected from the cathode of said triode to said tie conductor.

EMILE LABIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

